Dépouillements

Experimental phase diagram determination and thermodynamic assessment of the Gd2O3–CoO system / T. Ivas in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4077–4087 Titre : Experimental phase diagram determination and thermodynamic assessment of the Gd2O3–CoO system Type de document : texte imprimé Auteurs : T. Ivas, Auteur ; A.N. Grundy, Auteur ; E. Povoden, Auteur Année de publication : 2011 Article en page(s) : pp. 4077–4087 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : GdCoO3  Solid  solubilities  (Gd2O3,  CoO)  SOFC  CALPHAD Résumé : New phase diagram data and a thermodynamic assessment of the Gd2O3–CoO system using the CALPHAD approach are presented, giving liquidus data and mutual solid solubilities of Co in Gd2O3 and Gd in CoO. The thermodynamic model parameters for the ternary Gd–Co–perovskite phase and for the mutual solid solubilities of Co in Gd2O3 and Gd in CoO are optimized to reproduce these new experimental data, as well as phase diagram data from literature. The Gd2O3–CoO phase diagram is refined based on the results of experiments using combined differential thermal analysis and thermogravimetry, scanning electron microscopy and X-ray diffraction techniques. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001643 [article] Experimental phase diagram determination and thermodynamic assessment of the Gd2O3–CoO system [texte imprimé] / T. Ivas, Auteur ; A.N. Grundy, Auteur ; E. Povoden, Auteur . - 2011 . - pp. 4077–4087. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4077–4087 Mots-clés : GdCoO3  Solid  solubilities  (Gd2O3,  CoO)  SOFC  CALPHAD Résumé : New phase diagram data and a thermodynamic assessment of the Gd2O3–CoO system using the CALPHAD approach are presented, giving liquidus data and mutual solid solubilities of Co in Gd2O3 and Gd in CoO. The thermodynamic model parameters for the ternary Gd–Co–perovskite phase and for the mutual solid solubilities of Co in Gd2O3 and Gd in CoO are optimized to reproduce these new experimental data, as well as phase diagram data from literature. The Gd2O3–CoO phase diagram is refined based on the results of experiments using combined differential thermal analysis and thermogravimetry, scanning electron microscopy and X-ray diffraction techniques. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001643

Dynamic self-organization in Cu alloys under ion irradiation / S. W. Chee in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4088–4099 Titre : Dynamic self-organization in Cu alloys under ion irradiation Type de document : texte imprimé Auteurs : S. W. Chee, Auteur ; B. Stumphy, Auteur ; N.Q. Vo, Auteur Année de publication : 2011 Article en page(s) : pp. 4088–4099 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Copper  alloys  Nanocrystalline  materials  Phase  separation  Radiation  effects  Self-organization  and  patterning Résumé : Phase separation in dilute Cu(1–x)Mx films under irradiation with 1.8 MeV Kr+ ions at elevated temperatures has been studied for 0.10 < x < 0.15 and M = Ag, Co, Fe, Mo and Nb. In all systems compositional patterning was observed on a mesoscopic length scale within a fixed temperature interval. At lower temperatures most of the alloys formed nearly homogeneous solid solutions, while at higher temperatures these same alloys underwent macroscopic phase separation. The upper temperature limit for patterning increased with decreasing solute diffusivity in the Cu matrix, reported in the absence of irradiation. The heat of mixing of the alloy, however, also played a role in the patterning behavior. For Cu90Mo10, which has a high positive heat of mixing, no upper or lower temperature limits for patterning were observed. Molecular dynamics computer simulations reported here explain why Cu90Mo10 behaves differently from the other alloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001941 [article] Dynamic self-organization in Cu alloys under ion irradiation [texte imprimé] / S. W. Chee, Auteur ; B. Stumphy, Auteur ; N.Q. Vo, Auteur . - 2011 . - pp. 4088–4099. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4088–4099 Mots-clés : Copper  alloys  Nanocrystalline  materials  Phase  separation  Radiation  effects  Self-organization  and  patterning Résumé : Phase separation in dilute Cu(1–x)Mx films under irradiation with 1.8 MeV Kr+ ions at elevated temperatures has been studied for 0.10 < x < 0.15 and M = Ag, Co, Fe, Mo and Nb. In all systems compositional patterning was observed on a mesoscopic length scale within a fixed temperature interval. At lower temperatures most of the alloys formed nearly homogeneous solid solutions, while at higher temperatures these same alloys underwent macroscopic phase separation. The upper temperature limit for patterning increased with decreasing solute diffusivity in the Cu matrix, reported in the absence of irradiation. The heat of mixing of the alloy, however, also played a role in the patterning behavior. For Cu90Mo10, which has a high positive heat of mixing, no upper or lower temperature limits for patterning were observed. Molecular dynamics computer simulations reported here explain why Cu90Mo10 behaves differently from the other alloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001941

Friction and wear mechanisms in MoS2/Sb2O3/Au nanocomposite coatings / T.W. Scharf in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4100–4109 Titre : Friction and wear mechanisms in MoS2/Sb2O3/Au nanocomposite coatings Type de document : texte imprimé Auteurs : T.W. Scharf, Auteur ; P.G. Kotula, Auteur ; S.V. Prasad, Auteur Année de publication : 2011 Article en page(s) : pp. 4100–4109 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Coatings  Thin  films  Nanocomposites  Wear  Friction Résumé : Fundamental phenomena governing the tribological mechanisms in sputter deposited amorphous MoS2/Sb2O3/Au nanocomposite coatings are reported. In dry environments the nanocomposite has the same low friction coefficient as pure MoS2 (∼0.007). However, unlike pure MoS2 coatings, which wear through in air (50% relative humidity), the composite coatings showed minimal wear, with wear factors of ∼1.2–1.4 × 10−7 mm3 Nm−1 in both dry nitrogen and air. The coatings exhibited non-Amontonian friction behavior, with the friction coefficient decreasing with increasing Hertzian contact stress. Cross-sectional transmission electron microscopy of wear surfaces revealed that frictional contact resulted in an amorphous to crystalline transformation in MoS2 with 2H-basal (0 0 0 2) planes aligned parallel to the direction of sliding. In air the wear surface and subsurface regions exhibited islands of Au. The mating transfer films were also comprised of (0 0 0 2)-oriented basal planes of MoS2, resulting in predominantly self-mated “basal on basal” interfacial sliding and, thus, low friction and wear. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001989 [article] Friction and wear mechanisms in MoS2/Sb2O3/Au nanocomposite coatings [texte imprimé] / T.W. Scharf, Auteur ; P.G. Kotula, Auteur ; S.V. Prasad, Auteur . - 2011 . - pp. 4100–4109. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4100–4109 Mots-clés : Coatings  Thin  films  Nanocomposites  Wear  Friction Résumé : Fundamental phenomena governing the tribological mechanisms in sputter deposited amorphous MoS2/Sb2O3/Au nanocomposite coatings are reported. In dry environments the nanocomposite has the same low friction coefficient as pure MoS2 (∼0.007). However, unlike pure MoS2 coatings, which wear through in air (50% relative humidity), the composite coatings showed minimal wear, with wear factors of ∼1.2–1.4 × 10−7 mm3 Nm−1 in both dry nitrogen and air. The coatings exhibited non-Amontonian friction behavior, with the friction coefficient decreasing with increasing Hertzian contact stress. Cross-sectional transmission electron microscopy of wear surfaces revealed that frictional contact resulted in an amorphous to crystalline transformation in MoS2 with 2H-basal (0 0 0 2) planes aligned parallel to the direction of sliding. In air the wear surface and subsurface regions exhibited islands of Au. The mating transfer films were also comprised of (0 0 0 2)-oriented basal planes of MoS2, resulting in predominantly self-mated “basal on basal” interfacial sliding and, thus, low friction and wear. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001989

Shearing of γ′ precipitates by a〈1 1 2〉 dislocation ribbons in Ni-base superalloys / V.A. Vorontsov in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4110–4119 Titre : Shearing of γ′ precipitates by a〈1 1 2〉 dislocation ribbons in Ni-base superalloys : A phase field approach Type de document : texte imprimé Auteurs : V.A. Vorontsov, Auteur ; C. Shen, Auteur ; Y. Wang, Auteur Année de publication : 2011 Article en page(s) : pp. 4110–4119 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Primary  creep  Dislocation  dissociation  Phase  field  Shockley  partials  Stacking  faults Résumé : The phase field model of dislocations has been used to study the propagation of dislocation ribbons with an overall Burgers vector of a〈1 1 2〉 through a simulated Ni-base superalloy. The driving force for dislocation dissociation reactions and formation of planar faults is incorporated into the free energy functional using periodic functions specially fitted to ab initio γ-surface data. The model shows that the mechanism of cutting of the γ′ precipitates by these ribbons exhibits significant dependence on stress magnitude, orientation and precipitate shape. In the case of mixed screw–edge ribbons a change of shearing mode is observed, from stacking fault shear to anti-phase boundary shear, when the applied stress approaches the yield of the material. This transition is absent in pure edge ribbons. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001990 [article] Shearing of γ′ precipitates by a〈1 1 2〉 dislocation ribbons in Ni-base superalloys : A phase field approach [texte imprimé] / V.A. Vorontsov, Auteur ; C. Shen, Auteur ; Y. Wang, Auteur . - 2011 . - pp. 4110–4119. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4110–4119 Mots-clés : Primary  creep  Dislocation  dissociation  Phase  field  Shockley  partials  Stacking  faults Résumé : The phase field model of dislocations has been used to study the propagation of dislocation ribbons with an overall Burgers vector of a〈1 1 2〉 through a simulated Ni-base superalloy. The driving force for dislocation dissociation reactions and formation of planar faults is incorporated into the free energy functional using periodic functions specially fitted to ab initio γ-surface data. The model shows that the mechanism of cutting of the γ′ precipitates by these ribbons exhibits significant dependence on stress magnitude, orientation and precipitate shape. In the case of mixed screw–edge ribbons a change of shearing mode is observed, from stacking fault shear to anti-phase boundary shear, when the applied stress approaches the yield of the material. This transition is absent in pure edge ribbons. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410001990

Structural and compositional homogeneity of InAlN epitaxial layers nearly lattice-matched to GaN / J.M. Mánuel in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4120–4125 Titre : Structural and compositional homogeneity of InAlN epitaxial layers nearly lattice-matched to GaN Type de document : texte imprimé Auteurs : J.M. Mánuel, Auteur ; F.M. Morales, Auteur ; J.G. Lozano, Auteur Année de publication : 2011 Article en page(s) : pp. 4120–4125 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Compound  semiconductor  (InAlN)  Lattice-matched  Elastic  behavior  Transmission  electron  microscopy  (TEM)  Secondary  ion  mass  spectroscopy  (SIMS) Résumé : A group of InAlN films was fabricated by molecular beam epitaxy and investigated by X-ray diffraction, transmission electron microscopy and element nano-analyses. All top InxAl1−xN layers have compositions around lateral lattice-matching to GaN (x ≈ 0.18) and are pseudomorphic. For a growth rate of 350 nm h−1, each InAlN film separated into two sublayers with different In/Al-ratios. Micrographs reveal sharp transitions both at the InAlN/GaN and at the InAlN/InAlN interfaces. In contrast to these separated layers, an optimized epitaxy using an AlN interlayer and a lower growth rate, 100 nm h−1, enabled the fabrication of a single-phase InxAl1−xN layer on GaN, homogeneous on a nanoscopic scale. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002077 [article] Structural and compositional homogeneity of InAlN epitaxial layers nearly lattice-matched to GaN [texte imprimé] / J.M. Mánuel, Auteur ; F.M. Morales, Auteur ; J.G. Lozano, Auteur . - 2011 . - pp. 4120–4125. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4120–4125 Mots-clés : Compound  semiconductor  (InAlN)  Lattice-matched  Elastic  behavior  Transmission  electron  microscopy  (TEM)  Secondary  ion  mass  spectroscopy  (SIMS) Résumé : A group of InAlN films was fabricated by molecular beam epitaxy and investigated by X-ray diffraction, transmission electron microscopy and element nano-analyses. All top InxAl1−xN layers have compositions around lateral lattice-matching to GaN (x ≈ 0.18) and are pseudomorphic. For a growth rate of 350 nm h−1, each InAlN film separated into two sublayers with different In/Al-ratios. Micrographs reveal sharp transitions both at the InAlN/GaN and at the InAlN/InAlN interfaces. In contrast to these separated layers, an optimized epitaxy using an AlN interlayer and a lower growth rate, 100 nm h−1, enabled the fabrication of a single-phase InxAl1−xN layer on GaN, homogeneous on a nanoscopic scale. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002077

Microstructure–property relationship in textured ZnO-based varistors / İ. Özgür Özer in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4126–4136 Titre : Microstructure–property relationship in textured ZnO-based varistors Type de document : texte imprimé Auteurs : İ. Özgür Özer, Auteur ; Ender Suvaci, Auteur ; Slavko Bernik, Auteur Année de publication : 2011 Article en page(s) : pp. 4126–4136 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Zinc  oxide  Texture  Electrical  properties  Electron  backscattering  diffraction Résumé : The relationship between microstructure texturing and electrical characteristics of a ZnO-based varistor system was investigated in comparison with a varistor system having the same chemical composition but conventional microstructure. Highly textured ZnO-based varistors were produced via the templated grain growth (TGG) technique. Stereological analysis, electron back-scattered diffractometry (EBSD) and X-ray diffractometry (XRD) were conducted to analyze texture development and orientation distribution. The degree of orientation, r, calculated from the (0 0 0 1) EBSD pole figure, was 0.34; the texture fraction, f (Lotgering factor), calculated from the XRD data, was 0.98 for the samples produced via TGG. The threshold voltages were found to be anisotropic, consistent with the observed morphological texture. The non-linear coefficients, α, did not exhibit a significant difference as a function of direction, even in the highly textured samples. However, different types of grain boundary characteristics depending on the direction were identified with 0.42, 0.69 and 1.14 eV Schottky barrier heights. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002090 [article] Microstructure–property relationship in textured ZnO-based varistors [texte imprimé] / İ. Özgür Özer, Auteur ; Ender Suvaci, Auteur ; Slavko Bernik, Auteur . - 2011 . - pp. 4126–4136. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4126–4136 Mots-clés : Zinc  oxide  Texture  Electrical  properties  Electron  backscattering  diffraction Résumé : The relationship between microstructure texturing and electrical characteristics of a ZnO-based varistor system was investigated in comparison with a varistor system having the same chemical composition but conventional microstructure. Highly textured ZnO-based varistors were produced via the templated grain growth (TGG) technique. Stereological analysis, electron back-scattered diffractometry (EBSD) and X-ray diffractometry (XRD) were conducted to analyze texture development and orientation distribution. The degree of orientation, r, calculated from the (0 0 0 1) EBSD pole figure, was 0.34; the texture fraction, f (Lotgering factor), calculated from the XRD data, was 0.98 for the samples produced via TGG. The threshold voltages were found to be anisotropic, consistent with the observed morphological texture. The non-linear coefficients, α, did not exhibit a significant difference as a function of direction, even in the highly textured samples. However, different types of grain boundary characteristics depending on the direction were identified with 0.42, 0.69 and 1.14 eV Schottky barrier heights. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002090

Sliding wear of nanocrystalline Ni–W / Timothy J. Rupert in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4137–4148 Titre : Sliding wear of nanocrystalline Ni–W : Structural evolution and the apparent breakdown of Archard scaling Type de document : texte imprimé Auteurs : Timothy J. Rupert, Auteur ; Christopher A. Schuh, Auteur Année de publication : 2011 Article en page(s) : pp. 4137–4148 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanocrystalline  materials  Wear  Mechanical  properties  Ni–W  alloys  Grain  boundary  migration Résumé : Sliding wear of nanocrystalline Ni–W alloys with grain sizes of 3–47 nm, a range which spans the transition in deformation mechanisms from intra- to inter-granular, has been studied through pin-on-disk wear testing. The extreme conditions produced during sliding wear are found to result in structural evolution and a deviation from Archard scaling for the finest grain sizes; in the finest nanocrystalline materials wear resistance is higher than would be expected based on hardness alone. The repetitive sliding load is found to lead to a modest amount of grain growth and grain boundary relaxation, which in turn leads to local hardening in the wear track. Analysis of the dynamic microstructure suggests that it is produced primarily as a result of local plasticity and is not principally due to frictional heating. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002119 [article] Sliding wear of nanocrystalline Ni–W : Structural evolution and the apparent breakdown of Archard scaling [texte imprimé] / Timothy J. Rupert, Auteur ; Christopher A. Schuh, Auteur . - 2011 . - pp. 4137–4148. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4137–4148 Mots-clés : Nanocrystalline  materials  Wear  Mechanical  properties  Ni–W  alloys  Grain  boundary  migration Résumé : Sliding wear of nanocrystalline Ni–W alloys with grain sizes of 3–47 nm, a range which spans the transition in deformation mechanisms from intra- to inter-granular, has been studied through pin-on-disk wear testing. The extreme conditions produced during sliding wear are found to result in structural evolution and a deviation from Archard scaling for the finest grain sizes; in the finest nanocrystalline materials wear resistance is higher than would be expected based on hardness alone. The repetitive sliding load is found to lead to a modest amount of grain growth and grain boundary relaxation, which in turn leads to local hardening in the wear track. Analysis of the dynamic microstructure suggests that it is produced primarily as a result of local plasticity and is not principally due to frictional heating. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002119

Microstructural stability in multi-alloy systems / X. Pan in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4149–4159 Titre : Microstructural stability in multi-alloy systems : Nanostructured two-phase, dual alloy multilayers Type de document : texte imprimé Auteurs : X. Pan, Auteur ; N. Zhou, Auteur ; J.E. Morral, Auteur Année de publication : 2011 Article en page(s) : pp. 4149–4159 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Interdiffusion  Precipitate-free  zone  Diffusion  path  Simulation  Phase  field Résumé : Interdiffusion and microstructural stability in multilayers consisting of two nanostructured two-phase alloys were investigated using phase field simulations. A prototype ternary system containing a miscibility gap was used as the model system. Alloys with various compositions within the miscibility gap were chosen to form 20 μm bilayer repeating units in the multilayers. The initial microstructures in the alloys were produced by spinodal decomposition, which yielded a uniform distribution of precipitates having an average diameter of about 50 nm. Two types of multilayers were investigated; one in which the alloys in the repeating unit had the same matrix phase and the other in which the alloys had a different matrix phase. In general the microstructural instability measured as the size of the reaction zone increased with the increase in composition difference between the two initial alloys and in atomic mobility difference between the diffusing species. In particular, when the matrix phase was the same a precipitate-free zone (i.e. a single-phase layer) and a coarse interconnected precipitate zone formed at the interface between the two alloys, while when the matrix phase differed two precipitate-free zones formed at the interface. The microstructural instabilities were analyzed in terms of variations in the effective diffusivity with composition, which produced a singularity in the diffusion path at the initial alloy interface. The instability caused the diffusion path to exit the two phase region of the phase diagram and enter the single phase region. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002120 [article] Microstructural stability in multi-alloy systems : Nanostructured two-phase, dual alloy multilayers [texte imprimé] / X. Pan, Auteur ; N. Zhou, Auteur ; J.E. Morral, Auteur . - 2011 . - pp. 4149–4159. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4149–4159 Mots-clés : Interdiffusion  Precipitate-free  zone  Diffusion  path  Simulation  Phase  field Résumé : Interdiffusion and microstructural stability in multilayers consisting of two nanostructured two-phase alloys were investigated using phase field simulations. A prototype ternary system containing a miscibility gap was used as the model system. Alloys with various compositions within the miscibility gap were chosen to form 20 μm bilayer repeating units in the multilayers. The initial microstructures in the alloys were produced by spinodal decomposition, which yielded a uniform distribution of precipitates having an average diameter of about 50 nm. Two types of multilayers were investigated; one in which the alloys in the repeating unit had the same matrix phase and the other in which the alloys had a different matrix phase. In general the microstructural instability measured as the size of the reaction zone increased with the increase in composition difference between the two initial alloys and in atomic mobility difference between the diffusing species. In particular, when the matrix phase was the same a precipitate-free zone (i.e. a single-phase layer) and a coarse interconnected precipitate zone formed at the interface between the two alloys, while when the matrix phase differed two precipitate-free zones formed at the interface. The microstructural instabilities were analyzed in terms of variations in the effective diffusivity with composition, which produced a singularity in the diffusion path at the initial alloy interface. The instability caused the diffusion path to exit the two phase region of the phase diagram and enter the single phase region. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002120

Phase compositions, nanoscale microstructures and thermoelectric properties in Ag2−ySbyTe1+y alloys with precipitated Sb2Te3 plates / S.N. Zhang in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4160–4169 Titre : Phase compositions, nanoscale microstructures and thermoelectric properties in Ag2−ySbyTe1+y alloys with precipitated Sb2Te3 plates Type de document : texte imprimé Auteurs : S.N. Zhang, Auteur ; T.J. Zhu, Auteur ; S.H. Yang, Auteur Année de publication : 2011 Article en page(s) : pp. 4160–4169 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Thermoelectric  materials  Thermoelectric  properties  Silver  antimony  tellurides  Nanostructure Résumé : Nonstoichiometric ternary thermoelectric materials Ag2−ySbyTe1+y (y = 1.26, 1.29, 1.32, 1.35, and 1.38) were prepared by a direct melt-quench and hot press process. In situ composites of AgSbTe2 and Sb2Te3 were obtained over the entire composition range with a typical Widmanstätten pattern. Thermoelectric properties were measured from 300 K to 673 K, which changed systematically with Sb2Te3 ratio. The phase transition occurring at about 633 K, forming the single phased AgSbTe2, can significantly influence the electrical transport properties. Various crystallographic defects in different scales, such as atomic ordering, nanodomains, dislocations and stacking faults, have been observed by high-resolution transmission electron microscopy and their influences on lattice thermal conductivity have been discussed. Due to the extremely low thermal conductivity (about 0.6 W m−1 K−1) and large positive Seebeck coefficient of ∼250 μV K−1 detected in Ag0.71Sb1.29Te2.29, the maximum dimensionless figure of merit ZT of 1.37 was obtained at 600 K. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002132 [article] Phase compositions, nanoscale microstructures and thermoelectric properties in Ag2−ySbyTe1+y alloys with precipitated Sb2Te3 plates [texte imprimé] / S.N. Zhang, Auteur ; T.J. Zhu, Auteur ; S.H. Yang, Auteur . - 2011 . - pp. 4160–4169. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4160–4169 Mots-clés : Thermoelectric  materials  Thermoelectric  properties  Silver  antimony  tellurides  Nanostructure Résumé : Nonstoichiometric ternary thermoelectric materials Ag2−ySbyTe1+y (y = 1.26, 1.29, 1.32, 1.35, and 1.38) were prepared by a direct melt-quench and hot press process. In situ composites of AgSbTe2 and Sb2Te3 were obtained over the entire composition range with a typical Widmanstätten pattern. Thermoelectric properties were measured from 300 K to 673 K, which changed systematically with Sb2Te3 ratio. The phase transition occurring at about 633 K, forming the single phased AgSbTe2, can significantly influence the electrical transport properties. Various crystallographic defects in different scales, such as atomic ordering, nanodomains, dislocations and stacking faults, have been observed by high-resolution transmission electron microscopy and their influences on lattice thermal conductivity have been discussed. Due to the extremely low thermal conductivity (about 0.6 W m−1 K−1) and large positive Seebeck coefficient of ∼250 μV K−1 detected in Ag0.71Sb1.29Te2.29, the maximum dimensionless figure of merit ZT of 1.37 was obtained at 600 K. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002132

Phase-field simulations with inhomogeneous elasticity / Guillaume Boussinot in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4170–4181 Titre : Phase-field simulations with inhomogeneous elasticity : Comparison with an atomic-scale method and application to superalloys Type de document : texte imprimé Auteurs : Guillaume Boussinot, Auteur ; Yann Le Bouar, Auteur ; Alphonse Finel, Auteur Année de publication : 2011 Article en page(s) : pp. 4170–4181 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Phase-field  models  Phase  transformations  Elastic  behavior  Coarsening  Mean  field  analysis Résumé : We present a 2D and 3D phase-field analysis of microstructure evolution in the presence of a lattice misfit and with inhomogeneous elastic constants. The method is first critically compared with a Monte Carlo modeling at the atomic scale. We then apply the phase-field model to the Ni–Al system under external load along a cubic axis. We find that the microstructure becomes anisotropic and that the situation qualitatively differs depending on the sign of the applied stress. The microstructure evolution operates mainly by shape changes and alignments of precipitates, but also by splitting of precipitates initially elongated along directions perpendicular to the stress-induced, elastically favorable directions. The final microstructure is finally qualitatively analyzed in terms of a mean field theory in which the elastic inhomogeneity is embedded into an effective eigenstrain. This analysis leads to a simple formulation which can be used to easily predict the coherent microstructural anisotropy induced by any external loading condition. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002144 [article] Phase-field simulations with inhomogeneous elasticity : Comparison with an atomic-scale method and application to superalloys [texte imprimé] / Guillaume Boussinot, Auteur ; Yann Le Bouar, Auteur ; Alphonse Finel, Auteur . - 2011 . - pp. 4170–4181. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4170–4181 Mots-clés : Phase-field  models  Phase  transformations  Elastic  behavior  Coarsening  Mean  field  analysis Résumé : We present a 2D and 3D phase-field analysis of microstructure evolution in the presence of a lattice misfit and with inhomogeneous elastic constants. The method is first critically compared with a Monte Carlo modeling at the atomic scale. We then apply the phase-field model to the Ni–Al system under external load along a cubic axis. We find that the microstructure becomes anisotropic and that the situation qualitatively differs depending on the sign of the applied stress. The microstructure evolution operates mainly by shape changes and alignments of precipitates, but also by splitting of precipitates initially elongated along directions perpendicular to the stress-induced, elastically favorable directions. The final microstructure is finally qualitatively analyzed in terms of a mean field theory in which the elastic inhomogeneity is embedded into an effective eigenstrain. This analysis leads to a simple formulation which can be used to easily predict the coherent microstructural anisotropy induced by any external loading condition. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002144

Elastic limit for surface step dislocation nucleation in face-centered cubic metals / S. Brochard in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4182–4190 Titre : Elastic limit for surface step dislocation nucleation in face-centered cubic metals : Temperature and step height dependence Type de document : texte imprimé Auteurs : S. Brochard, Auteur ; P. Hirel, Auteur ; L. Pizzagalli, Auteur Année de publication : 2011 Article en page(s) : pp. 4182–4190 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dislocation  nucleation  Plastic  deformation  MD  simulations  Surface  Thermally  activated  processes Résumé : The influences of surface step state and temperature on the elastic limit for dislocation nucleation from a surface step were analyzed by means of atomic scale simulations in face-centered cubic metals. When varying the step height, two regimes were found: for smaller steps, local effects dominate, whereas for larger steps, the stress concentration prevails. The differences observed for the elastic limit were correlated to relevant properties of the different potentials. Finally, for aluminum, the implication of the activation parameters in the nucleation strain was studied in greater detail. This study is particularly relevant to nanostructures, where plasticity is most often governed by dislocation nucleation rather than dislocation multiplication. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002156 [article] Elastic limit for surface step dislocation nucleation in face-centered cubic metals : Temperature and step height dependence [texte imprimé] / S. Brochard, Auteur ; P. Hirel, Auteur ; L. Pizzagalli, Auteur . - 2011 . - pp. 4182–4190. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4182–4190 Mots-clés : Dislocation  nucleation  Plastic  deformation  MD  simulations  Surface  Thermally  activated  processes Résumé : The influences of surface step state and temperature on the elastic limit for dislocation nucleation from a surface step were analyzed by means of atomic scale simulations in face-centered cubic metals. When varying the step height, two regimes were found: for smaller steps, local effects dominate, whereas for larger steps, the stress concentration prevails. The differences observed for the elastic limit were correlated to relevant properties of the different potentials. Finally, for aluminum, the implication of the activation parameters in the nucleation strain was studied in greater detail. This study is particularly relevant to nanostructures, where plasticity is most often governed by dislocation nucleation rather than dislocation multiplication. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002156

Novel approaches to determining residual stresses by ultramicroindentation techniques / E. Frutos in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4191–4198 Titre : Novel approaches to determining residual stresses by ultramicroindentation techniques : Application to sandblasted austenitic stainless steel Type de document : texte imprimé Auteurs : E. Frutos, Auteur ; M. Multigner, Auteur ; J.L. González-Carrasco, Auteur Année de publication : 2011 Article en page(s) : pp. 4191–4198 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Sand  blasting  Microindentation  Austenitic  steels  Residual  stresses  Microstructure Résumé : This research addresses the determination of residual stresses in sandblasted austenitic steel by ultramicroindentation techniques using a sharp indenter, of which the sensitivity to residual stress effects is said to be inferior to that of spherical ones. The introduction of an angular correction in the model of Wang et al. which relates variations in the maximum load to the presence of residual stresses is proposed. Similarly, the contribution to the hardness of grain size refinement and work hardening, developed as a consequence of the severe plastic deformation during blasting, is determined in order to avoid overestimation of the residual stresses. Measurements were performed on polished cross sections along a length of several microns, thus obtaining a profile of the residual stresses. Results show good agreement with those obtained by synchrotron radiation on the same specimens, which validates the method and demonstrates that microindentation using sharp indenters may be sensitive to the residual stress effect. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002168 [article] Novel approaches to determining residual stresses by ultramicroindentation techniques : Application to sandblasted austenitic stainless steel [texte imprimé] / E. Frutos, Auteur ; M. Multigner, Auteur ; J.L. González-Carrasco, Auteur . - 2011 . - pp. 4191–4198. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4191–4198 Mots-clés : Sand  blasting  Microindentation  Austenitic  steels  Residual  stresses  Microstructure Résumé : This research addresses the determination of residual stresses in sandblasted austenitic steel by ultramicroindentation techniques using a sharp indenter, of which the sensitivity to residual stress effects is said to be inferior to that of spherical ones. The introduction of an angular correction in the model of Wang et al. which relates variations in the maximum load to the presence of residual stresses is proposed. Similarly, the contribution to the hardness of grain size refinement and work hardening, developed as a consequence of the severe plastic deformation during blasting, is determined in order to avoid overestimation of the residual stresses. Measurements were performed on polished cross sections along a length of several microns, thus obtaining a profile of the residual stresses. Results show good agreement with those obtained by synchrotron radiation on the same specimens, which validates the method and demonstrates that microindentation using sharp indenters may be sensitive to the residual stress effect. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002168

Phase separation mediated devitrification of Al88Y7Fe5 glasses / K.K. Sahu in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4199–4206 Titre : Phase separation mediated devitrification of Al88Y7Fe5 glasses Type de document : texte imprimé Auteurs : K.K. Sahu, Auteur ; N.A. Mauro, Auteur ; L. Longstreth-Spoor, Auteur Année de publication : 2011 Article en page(s) : pp. 4199–4206 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Coarsening  Aluminum  alloys  Phase  separation  Nucleation  and  growth  Metallic  glass Résumé : The mechanisms responsible for the nanoscale devitrification of Al-based metallic glasses are unclear. A particularly well-studied case is Al88Y7Fe5, where non-isothermal differential scanning calorimetry (DSC) measurements show an exothermic peak that is consistent with glass devitrification to α-Al, but with no glass transition. Additionally, isothermal DSC studies show a monotonic decrease in enthalpy release with annealing, a feature generally taken to indicate grain coarsening. The results of coordinated DSC, bright field transmission electron microscopy, in situ electrical resistivity and atom probe tomography (APT) studies of Al88Y7Fe5 support a nucleation/growth-based crystallization process. The APT data indicate the presence of sub-nanometer pure Al zones and coarser scale (separation distance ∼74–126 nm) Al-rich regions in the glass. The pure Al zones dispersed in the Al-rich regions appear to catalyze α-Al nucleation, explaining the high nucleation rates. The solute-rich regions between the Al-rich regions inhibit long-range diffusion, explaining the low growth rates. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000217X [article] Phase separation mediated devitrification of Al88Y7Fe5 glasses [texte imprimé] / K.K. Sahu, Auteur ; N.A. Mauro, Auteur ; L. Longstreth-Spoor, Auteur . - 2011 . - pp. 4199–4206. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4199–4206 Mots-clés : Coarsening  Aluminum  alloys  Phase  separation  Nucleation  and  growth  Metallic  glass Résumé : The mechanisms responsible for the nanoscale devitrification of Al-based metallic glasses are unclear. A particularly well-studied case is Al88Y7Fe5, where non-isothermal differential scanning calorimetry (DSC) measurements show an exothermic peak that is consistent with glass devitrification to α-Al, but with no glass transition. Additionally, isothermal DSC studies show a monotonic decrease in enthalpy release with annealing, a feature generally taken to indicate grain coarsening. The results of coordinated DSC, bright field transmission electron microscopy, in situ electrical resistivity and atom probe tomography (APT) studies of Al88Y7Fe5 support a nucleation/growth-based crystallization process. The APT data indicate the presence of sub-nanometer pure Al zones and coarser scale (separation distance ∼74–126 nm) Al-rich regions in the glass. The pure Al zones dispersed in the Al-rich regions appear to catalyze α-Al nucleation, explaining the high nucleation rates. The solute-rich regions between the Al-rich regions inhibit long-range diffusion, explaining the low growth rates. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S135964541000217X

Evolution of specific surface area with solid fraction during solidification / L. Ratke in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4207–4211 Titre : Evolution of specific surface area with solid fraction during solidification Type de document : texte imprimé Auteurs : L. Ratke, Auteur ; A. Genau, Auteur Année de publication : 2011 Article en page(s) : pp. 4207–4211 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Fraction  solid  Specific  surface  area  Growth  Coalescence Résumé : The specific surface area varies with solid fraction during phase transformation from liquid to solid. The few measurements available show a non-linear dependence of the specific surface area on the solid fraction, with an initial increase as the amount of solid increases, followed by a decrease as the system moves toward complete transformation. We derive a simple model for this behaviour assuming a combination of growth and coalescence. We obtain a relation exhibiting an increase with the square root of fraction solid at low volume fractions, independent of a growth law, and a decrease at higher volume fractions which depends on the model chosen to describe the coalescence of dendrites. By choosing an appropriate constant, the model accurately describes recent data presented by Limodin and co-workers. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002181 [article] Evolution of specific surface area with solid fraction during solidification [texte imprimé] / L. Ratke, Auteur ; A. Genau, Auteur . - 2011 . - pp. 4207–4211. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4207–4211 Mots-clés : Fraction  solid  Specific  surface  area  Growth  Coalescence Résumé : The specific surface area varies with solid fraction during phase transformation from liquid to solid. The few measurements available show a non-linear dependence of the specific surface area on the solid fraction, with an initial increase as the amount of solid increases, followed by a decrease as the system moves toward complete transformation. We derive a simple model for this behaviour assuming a combination of growth and coalescence. We obtain a relation exhibiting an increase with the square root of fraction solid at low volume fractions, independent of a growth law, and a decrease at higher volume fractions which depends on the model chosen to describe the coalescence of dendrites. By choosing an appropriate constant, the model accurately describes recent data presented by Limodin and co-workers. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002181

Shape memory properties of Ti–Nb–Mo biomedical alloys / Y. Al-Zain in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4212–4223 Titre : Shape memory properties of Ti–Nb–Mo biomedical alloys Type de document : texte imprimé Auteurs : Y. Al-Zain, Auteur ; H.Y. Kim, Auteur ; H. Hosoda, Auteur Année de publication : 2011 Article en page(s) : pp. 4212–4223 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Ti–Nb  Ti–Nb–Mo  Shape  memory  alloys  Superelasticity Résumé : Mo is added to Ti–Nb alloys in order to enhance their superelasticity. The shape memory properties of Ti–(12–28)Nb–(0–4)Mo alloys are investigated in this paper. The Ti–27Nb, Ti–24Nb–1Mo, Ti–21Nb–2Mo and Ti–18Nb–3Mo alloys exhibit the most stable superelasticity with a narrow stress hysteresis among Ti–Nb–Mo alloys with Mo contents of 0, 1, 2 and 3 at.%, respectively. The ternary alloys reveal better superelasticity due to a higher critical stress for slip deformation and a larger transformation strain. A Ti–15Nb–4Mo alloy heat-treated at 973 K undergoes (2 1 1)〈1 1 1〉-type twinning during tensile testing. Twinning is suppressed in the alloy heat-treated at 923 K due to the precipitation of the α phase, allowing the alloy to deform via a martensitic transformation process. The Ti–15Nb–4Mo alloy exhibits stable superelasticity with a critical stress for slip deformation of 582 MPa and a total recovery strain of 3.5%. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002296 [article] Shape memory properties of Ti–Nb–Mo biomedical alloys [texte imprimé] / Y. Al-Zain, Auteur ; H.Y. Kim, Auteur ; H. Hosoda, Auteur . - 2011 . - pp. 4212–4223. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4212–4223 Mots-clés : Ti–Nb  Ti–Nb–Mo  Shape  memory  alloys  Superelasticity Résumé : Mo is added to Ti–Nb alloys in order to enhance their superelasticity. The shape memory properties of Ti–(12–28)Nb–(0–4)Mo alloys are investigated in this paper. The Ti–27Nb, Ti–24Nb–1Mo, Ti–21Nb–2Mo and Ti–18Nb–3Mo alloys exhibit the most stable superelasticity with a narrow stress hysteresis among Ti–Nb–Mo alloys with Mo contents of 0, 1, 2 and 3 at.%, respectively. The ternary alloys reveal better superelasticity due to a higher critical stress for slip deformation and a larger transformation strain. A Ti–15Nb–4Mo alloy heat-treated at 973 K undergoes (2 1 1)〈1 1 1〉-type twinning during tensile testing. Twinning is suppressed in the alloy heat-treated at 923 K due to the precipitation of the α phase, allowing the alloy to deform via a martensitic transformation process. The Ti–15Nb–4Mo alloy exhibits stable superelasticity with a critical stress for slip deformation of 582 MPa and a total recovery strain of 3.5%. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002296

Structural changes and thermal properties of aluminium micro- and nano-powders / B. Rufino in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4224–4232 Titre : Structural changes and thermal properties of aluminium micro- and nano-powders Type de document : texte imprimé Auteurs : B. Rufino, Auteur ; M.-V. Coulet, Auteur ; R. Bouchet, Auteur Année de publication : 2011 Article en page(s) : pp. 4224–4232 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Aluminium  powders  Differential  scanning  calorimetry  Thermogravimetric  analysis  Neutron  diffraction  Thermal  dilatation Résumé : Structural and chemical properties of aluminium powders with size distribution in the micrometer and nanometer range are studied. The particles can be described by an aluminium core surrounded with an alumina layer which, depending on the passivation method, can be amorphous or constituted with small crystallites of γ-alumina. Using calorimetric measurements and in situ neutron diffraction experiments, the crystallization of the amorphous shell is evidenced and a tetragonal structure for the crystallized γ-alumina is proposed. The thermal expansion of the aluminium core is obtained by following the variation of the cell parameter with temperature. It is shown that, whatever is the size of particles, the thermal expansion of the metallic core is not affected by an alumina shell with a 3 ± 2 nm thickness. In contrast, when the thickness of the crystalline alumina shell exceeds 20 nm, strong strain effects are evidenced. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002302 [article] Structural changes and thermal properties of aluminium micro- and nano-powders [texte imprimé] / B. Rufino, Auteur ; M.-V. Coulet, Auteur ; R. Bouchet, Auteur . - 2011 . - pp. 4224–4232. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4224–4232 Mots-clés : Aluminium  powders  Differential  scanning  calorimetry  Thermogravimetric  analysis  Neutron  diffraction  Thermal  dilatation Résumé : Structural and chemical properties of aluminium powders with size distribution in the micrometer and nanometer range are studied. The particles can be described by an aluminium core surrounded with an alumina layer which, depending on the passivation method, can be amorphous or constituted with small crystallites of γ-alumina. Using calorimetric measurements and in situ neutron diffraction experiments, the crystallization of the amorphous shell is evidenced and a tetragonal structure for the crystallized γ-alumina is proposed. The thermal expansion of the aluminium core is obtained by following the variation of the cell parameter with temperature. It is shown that, whatever is the size of particles, the thermal expansion of the metallic core is not affected by an alumina shell with a 3 ± 2 nm thickness. In contrast, when the thickness of the crystalline alumina shell exceeds 20 nm, strong strain effects are evidenced. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002302

Constrained sintering of an air-plasma-sprayed thermal barrier coating / A.C.F. Cocks in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4233–4244 Titre : Constrained sintering of an air-plasma-sprayed thermal barrier coating Type de document : texte imprimé Auteurs : A.C.F. Cocks, Auteur ; N.A. Fleck, Auteur Année de publication : 2011 Article en page(s) : pp. 4233–4244 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Sintering  Coatings  Variational  methods  Micromechanical  modelling  Creep Résumé : A micromechanical model is presented for the constrained sintering of an air-plasma-sprayed, thermal barrier coating upon a thick superalloy substrate. The coating comprises random splats with intervening penny-shaped cracks. The crack faces make contact at asperities, which progressively sinter in-service by interfacial diffusion, accommodated by bulk creep. Diffusion is driven by the reduction in interfacial energy at the developing contacts and by the local asperity contact stress. At elevated operating temperature, both sintering and creep strains accumulate within the plane of the coating. The sensitivities of sintering rate and microstructure evolution rate to the kinetic parameters and thermodynamic driving forces are explored. It is demonstrated that the sintering response is governed by three independent timescales, as dictated by the material and geometric properties of the coating. Finally, the role of substrate constraint is assessed by comparing the rate of constrained sintering with that for free sintering. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002314 [article] Constrained sintering of an air-plasma-sprayed thermal barrier coating [texte imprimé] / A.C.F. Cocks, Auteur ; N.A. Fleck, Auteur . - 2011 . - pp. 4233–4244. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4233–4244 Mots-clés : Sintering  Coatings  Variational  methods  Micromechanical  modelling  Creep Résumé : A micromechanical model is presented for the constrained sintering of an air-plasma-sprayed, thermal barrier coating upon a thick superalloy substrate. The coating comprises random splats with intervening penny-shaped cracks. The crack faces make contact at asperities, which progressively sinter in-service by interfacial diffusion, accommodated by bulk creep. Diffusion is driven by the reduction in interfacial energy at the developing contacts and by the local asperity contact stress. At elevated operating temperature, both sintering and creep strains accumulate within the plane of the coating. The sensitivities of sintering rate and microstructure evolution rate to the kinetic parameters and thermodynamic driving forces are explored. It is demonstrated that the sintering response is governed by three independent timescales, as dictated by the material and geometric properties of the coating. Finally, the role of substrate constraint is assessed by comparing the rate of constrained sintering with that for free sintering. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002314

Aluminum Σ3 grain boundary sliding enhanced by vacancy diffusion / Ningning Du in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4245–4252 Titre : Aluminum Σ3 grain boundary sliding enhanced by vacancy diffusion Type de document : texte imprimé Auteurs : Ningning Du, Auteur ; Yue Qi, Auteur ; Paul E. Krajewski, Auteur Année de publication : 2011 Article en page(s) : pp. 4245–4252 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Molecular  dynamics  Grain  boundary  sliding  Aluminum  Superplasticity  Grain  boundary  structure Résumé : Grain boundary sliding is an important deformation mechanism for elevated temperature forming processes. Molecular dynamics simulations are used to investigate the effect of vacancies in the grain boundary vicinity on the sliding of Al bi-crystals at 750 K. The threshold stress for grain boundary sliding was computed for a variety of grain boundaries with different structures and energies. These structures included one symmetrical tilt grain boundary and five asymmetrical tilt grain boundaries. Without vacancies, low energy Σ3 grain boundaries exhibited significantly less sliding than other high energy grain boundaries. The addition of vacancies to Σ3 grain boundaries decreased the threshold stress for grain boundary sliding by increasing the grain boundary diffusivity. A higher concentration of vacancies enhanced this effect. The influence of vacancies on grain boundary diffusivity and grain boundary sliding was negligible for high energy grain boundaries, due to the already high atom mobility in these boundaries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002326 [article] Aluminum Σ3 grain boundary sliding enhanced by vacancy diffusion [texte imprimé] / Ningning Du, Auteur ; Yue Qi, Auteur ; Paul E. Krajewski, Auteur . - 2011 . - pp. 4245–4252. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4245–4252 Mots-clés : Molecular  dynamics  Grain  boundary  sliding  Aluminum  Superplasticity  Grain  boundary  structure Résumé : Grain boundary sliding is an important deformation mechanism for elevated temperature forming processes. Molecular dynamics simulations are used to investigate the effect of vacancies in the grain boundary vicinity on the sliding of Al bi-crystals at 750 K. The threshold stress for grain boundary sliding was computed for a variety of grain boundaries with different structures and energies. These structures included one symmetrical tilt grain boundary and five asymmetrical tilt grain boundaries. Without vacancies, low energy Σ3 grain boundaries exhibited significantly less sliding than other high energy grain boundaries. The addition of vacancies to Σ3 grain boundaries decreased the threshold stress for grain boundary sliding by increasing the grain boundary diffusivity. A higher concentration of vacancies enhanced this effect. The influence of vacancies on grain boundary diffusivity and grain boundary sliding was negligible for high energy grain boundaries, due to the already high atom mobility in these boundaries. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002326

Evolution of microstructure and microtexture during the hot deformation of Mg–3% Al / Étienne Martin in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4253–4266 Titre : Evolution of microstructure and microtexture during the hot deformation of Mg–3% Al Type de document : texte imprimé Auteurs : Étienne Martin, Auteur ; John J. Jonas, Auteur Année de publication : 2011 Article en page(s) : pp. 4253–4266 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Magnesium  Dynamic  recrystallization  Dislocation  boundaries  Orientation  imaging  microscopy  Misorientation  relationships Résumé : The orientation relationships associated with different mechanisms of new grain formation during the hot deformation of a Mg–3.4% Al–0.33% Mn alloy were investigated using electron back-scattered diffraction (EBSD) techniques. Compression tests were carried out at 350 °C with a strain rate of 0.001 s−1 on samples machined from extruded tubes. Three types of microstructural features were produced at this temperature: (i) microbands (MBs); (ii) bulged regions; (iii) new grains formed by continuous dynamic recrystallization (cDRX). The formation of the MBs is attributed to the collection of basal dislocations in the MB boundaries. Both the bulges as well as the new cDRX grains are formed as a result of dislocation-based processes that produce c-axis rotations toward the loading axis (i.e. away from the radial direction–transverse direction (RD–TD) plane). Once nuclei have formed, however, the new grains have their c-axes located fairly close to the RD–TD plane. In this way dynamic recrystallization leads to the retention of the main characteristics of the initial RD–TD texture. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002338 [article] Evolution of microstructure and microtexture during the hot deformation of Mg–3% Al [texte imprimé] / Étienne Martin, Auteur ; John J. Jonas, Auteur . - 2011 . - pp. 4253–4266. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4253–4266 Mots-clés : Magnesium  Dynamic  recrystallization  Dislocation  boundaries  Orientation  imaging  microscopy  Misorientation  relationships Résumé : The orientation relationships associated with different mechanisms of new grain formation during the hot deformation of a Mg–3.4% Al–0.33% Mn alloy were investigated using electron back-scattered diffraction (EBSD) techniques. Compression tests were carried out at 350 °C with a strain rate of 0.001 s−1 on samples machined from extruded tubes. Three types of microstructural features were produced at this temperature: (i) microbands (MBs); (ii) bulged regions; (iii) new grains formed by continuous dynamic recrystallization (cDRX). The formation of the MBs is attributed to the collection of basal dislocations in the MB boundaries. Both the bulges as well as the new cDRX grains are formed as a result of dislocation-based processes that produce c-axis rotations toward the loading axis (i.e. away from the radial direction–transverse direction (RD–TD) plane). Once nuclei have formed, however, the new grains have their c-axes located fairly close to the RD–TD plane. In this way dynamic recrystallization leads to the retention of the main characteristics of the initial RD–TD texture. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002338

Finite-element analysis for high-temperature deformation of bulk metallic glasses in a supercooled liquid region based on the free volume constitutive model / H-J. Jun in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4267–4280 Titre : Finite-element analysis for high-temperature deformation of bulk metallic glasses in a supercooled liquid region based on the free volume constitutive model Type de document : texte imprimé Auteurs : H-J. Jun, Auteur ; K.S. Lee, Auteur ; S.C. Yoon, Auteur Année de publication : 2011 Article en page(s) : pp. 4267–4280 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Bulk  metallic  glass  Free  volume  Constitutive  relation  Finite-element  method  Supercooled  liquid  region Résumé : A constitutive relation based on the free volume model was developed to describe the strain-rate-dependent deformation behavior of bulk metallic glasses (BMG) at temperatures within the supercooled liquid region (SLR). Validity of the present approach has consequently been assessed by comparing the numerical results obtained from finite-element analyses with the experimental results previously obtained from compression tests of Vitreloy-1 BMG alloy. Finite-element-method simulations combined with free volume constitutive relations were found to reproduce well the plastic deformation behavior of Vitreloy-1 alloy, exhibiting a Newtonian viscous flow without stress overshoot and also a non-Newtonian viscous flow with stress overshoot at temperatures within the SLR. The present approach appears to provide a powerful means of understanding plastic deformation behavior in relation to localized and uniform deformation and also of making reliable formability estimations of BMG alloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002363 [article] Finite-element analysis for high-temperature deformation of bulk metallic glasses in a supercooled liquid region based on the free volume constitutive model [texte imprimé] / H-J. Jun, Auteur ; K.S. Lee, Auteur ; S.C. Yoon, Auteur . - 2011 . - pp. 4267–4280. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4267–4280 Mots-clés : Bulk  metallic  glass  Free  volume  Constitutive  relation  Finite-element  method  Supercooled  liquid  region Résumé : A constitutive relation based on the free volume model was developed to describe the strain-rate-dependent deformation behavior of bulk metallic glasses (BMG) at temperatures within the supercooled liquid region (SLR). Validity of the present approach has consequently been assessed by comparing the numerical results obtained from finite-element analyses with the experimental results previously obtained from compression tests of Vitreloy-1 BMG alloy. Finite-element-method simulations combined with free volume constitutive relations were found to reproduce well the plastic deformation behavior of Vitreloy-1 alloy, exhibiting a Newtonian viscous flow without stress overshoot and also a non-Newtonian viscous flow with stress overshoot at temperatures within the SLR. The present approach appears to provide a powerful means of understanding plastic deformation behavior in relation to localized and uniform deformation and also of making reliable formability estimations of BMG alloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002363

(0 0 l)-oriented Bi2Sr2Co2Oy and Ca3Co4O9 films / Xuebin Zhu in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4281–4291 Titre : (0 0 l)-oriented Bi2Sr2Co2Oy and Ca3Co4O9 films : Self-assembly orientation and growth mechanism by chemical solution deposition Type de document : texte imprimé Auteurs : Xuebin Zhu, Auteur ; Dongqi Shi, Auteur ; Shixue Dou, Auteur Année de publication : 2011 Article en page(s) : pp. 4281–4291 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Self-assembly  Thermoelectric  Film  Chemical  solution  deposition Résumé : In this study, two typical cobaltate-based thermoelectric films, Bi2Sr2Co2Oy (BSC) and Ca3Co4O9 (CCO), with structures of [Bi2Sr2O4][CoO2]2 and [Ca2CoO3]RS[CoO2], respectively, are prepared by a simple chemical solution deposition on SrTiO3 (1 0 0), (1 1 0), and (1 1 1) single crystal substrates. X-ray results reveal that all films are c-axis oriented regardless of the orientation of the substrate, suggesting self-assembly orientation. Transmission electron microscopy reveals amorphous/delamination regions for BSC film on SrTiO3 (1 1 0), and the c-axis stripes of CCO on SrTiO3 (1 1 1) are inclined at 30° to the interface, whereas the c-axis stripes are parallel to the interfaces for other films. The growth mechanism is established, and the driving force for self-assembly c-axis orientation is attributed to the syneresis stress due to solvent evaporation. The microstructures and properties are also studied and discussed, with the conclusion that self-assembly c-axis oriented layered cobaltates films are good candidates for thermoelectric applications. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002375 [article] (0 0 l)-oriented Bi2Sr2Co2Oy and Ca3Co4O9 films : Self-assembly orientation and growth mechanism by chemical solution deposition [texte imprimé] / Xuebin Zhu, Auteur ; Dongqi Shi, Auteur ; Shixue Dou, Auteur . - 2011 . - pp. 4281–4291. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4281–4291 Mots-clés : Self-assembly  Thermoelectric  Film  Chemical  solution  deposition Résumé : In this study, two typical cobaltate-based thermoelectric films, Bi2Sr2Co2Oy (BSC) and Ca3Co4O9 (CCO), with structures of [Bi2Sr2O4][CoO2]2 and [Ca2CoO3]RS[CoO2], respectively, are prepared by a simple chemical solution deposition on SrTiO3 (1 0 0), (1 1 0), and (1 1 1) single crystal substrates. X-ray results reveal that all films are c-axis oriented regardless of the orientation of the substrate, suggesting self-assembly orientation. Transmission electron microscopy reveals amorphous/delamination regions for BSC film on SrTiO3 (1 1 0), and the c-axis stripes of CCO on SrTiO3 (1 1 1) are inclined at 30° to the interface, whereas the c-axis stripes are parallel to the interfaces for other films. The growth mechanism is established, and the driving force for self-assembly c-axis orientation is attributed to the syneresis stress due to solvent evaporation. The microstructures and properties are also studied and discussed, with the conclusion that self-assembly c-axis oriented layered cobaltates films are good candidates for thermoelectric applications. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002375

Thermal stability of nanocrystalline Pd81Zr19 / Brian K. VanLeeuwen in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4292–4297 Titre : Thermal stability of nanocrystalline Pd81Zr19 Type de document : texte imprimé Auteurs : Brian K. VanLeeuwen, Auteur ; Kristopher A. Darling, Auteur ; Carl C. Koch, Auteur Année de publication : 2011 Article en page(s) : pp. 4292–4297 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Nanocrystalline  materials  Grain  growth  Grain  boundary  energy  Grain  boundary  segregation  Solute  segregation Résumé : Grain growth stability in mechanically alloyed nanocrystalline Pd81Zr19 was investigated. Previous research suggested that the alloy is thermodynamically stable to very high temperatures. When X-ray diffraction (XRD) is used to estimate the grain size of annealed samples the alloy appears to have remarkable resistance to growth. Microscopy done here on the same alloy indicated that the XRD estimates are not accurate for samples annealed above 600 °C. It appears that when this alloy is annealed at high temperatures XRD peak broadening is retained for reasons that are unrelated to the grain size. The alloy still has much improved grain growth stability compared with pure Pd, but not as significant as suggested by the XRD results. A similar phenomenon was observed in Fe–Zr alloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002399 [article] Thermal stability of nanocrystalline Pd81Zr19 [texte imprimé] / Brian K. VanLeeuwen, Auteur ; Kristopher A. Darling, Auteur ; Carl C. Koch, Auteur . - 2011 . - pp. 4292–4297. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4292–4297 Mots-clés : Nanocrystalline  materials  Grain  growth  Grain  boundary  energy  Grain  boundary  segregation  Solute  segregation Résumé : Grain growth stability in mechanically alloyed nanocrystalline Pd81Zr19 was investigated. Previous research suggested that the alloy is thermodynamically stable to very high temperatures. When X-ray diffraction (XRD) is used to estimate the grain size of annealed samples the alloy appears to have remarkable resistance to growth. Microscopy done here on the same alloy indicated that the XRD estimates are not accurate for samples annealed above 600 °C. It appears that when this alloy is annealed at high temperatures XRD peak broadening is retained for reasons that are unrelated to the grain size. The alloy still has much improved grain growth stability compared with pure Pd, but not as significant as suggested by the XRD results. A similar phenomenon was observed in Fe–Zr alloys. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002399

Mechanical properties and determination of slip systems of the B2 YZn intermetallic compound / G.H. Cao in Acta materialia, Vol. 58 N° 12 (Juillet 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4298–4304 Titre : Mechanical properties and determination of slip systems of the B2 YZn intermetallic compound Type de document : texte imprimé Auteurs : G.H. Cao, Auteur ; A.T. Becker, Auteur ; Wu, D., Auteur Année de publication : 2011 Article en page(s) : pp. 4298–4304 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Intermetallics  Mechanical  properties  Slip  Transmission  electron  microscopy  (TEM)  YZn Résumé : Single crystal specimens of YZn (B2) were tested in tension at room temperature. Specimens with a [1 0 1] tensile axis orientation exhibited {0 1 1}〈1 0 0〉 primary slip and an ultimate tensile strength of 365 MPa at 3.7% elongation. Specimens with [0 0 1] and [1 1 1] tensile axis orientations showed no slip lines and fractured at a stress of 180 MPa at 3.3% and 130 MPa at 2.9% elongation, respectively. Transmission electron microscopy (TEM) examination of the Burger’s vector of dislocations in tensile tested specimens revealed 〈1 0 0〉-type dislocations. TEM analysis suggested that a secondary slip system, {0 0 1}〈1 0 0〉, may be active. Banded features with a {0 2 1} orientation were observed in deformed YZn; these may be slip traces produced by the cross-slip of 〈1 0 0〉 dislocations. Acting together, {0 1 1}〈1 0 0〉 and {0 0 1}〈1 0 0〉 slip provide only three independent slip systems, and no extra independent systems are provided by the cross-slip. This finding is consistent with the low ductility of YZn. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002405 [article] Mechanical properties and determination of slip systems of the B2 YZn intermetallic compound [texte imprimé] / G.H. Cao, Auteur ; A.T. Becker, Auteur ; Wu, D., Auteur . - 2011 . - pp. 4298–4304. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 12 (Juillet 2010) . - pp. 4298–4304 Mots-clés : Intermetallics  Mechanical  properties  Slip  Transmission  electron  microscopy  (TEM)  YZn Résumé : Single crystal specimens of YZn (B2) were tested in tension at room temperature. Specimens with a [1 0 1] tensile axis orientation exhibited {0 1 1}〈1 0 0〉 primary slip and an ultimate tensile strength of 365 MPa at 3.7% elongation. Specimens with [0 0 1] and [1 1 1] tensile axis orientations showed no slip lines and fractured at a stress of 180 MPa at 3.3% and 130 MPa at 2.9% elongation, respectively. Transmission electron microscopy (TEM) examination of the Burger’s vector of dislocations in tensile tested specimens revealed 〈1 0 0〉-type dislocations. TEM analysis suggested that a secondary slip system, {0 0 1}〈1 0 0〉, may be active. Banded features with a {0 2 1} orientation were observed in deformed YZn; these may be slip traces produced by the cross-slip of 〈1 0 0〉 dislocations. Acting together, {0 1 1}〈1 0 0〉 and {0 0 1}〈1 0 0〉 slip provide only three independent slip systems, and no extra independent systems are provided by the cross-slip. This finding is consistent with the low ductility of YZn. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410002405

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